An internal combustion engine burns fuel and air in a combustion chamber to generate power. Intake valves are operated by a camshaft in order to intake the air, and the air is drawn into the combustion chamber while the intake valves are opened. In addition, exhaust valves are operated by the camshaft, and combustion gas is exhausted from the combustion chamber while the exhaust valves are opened.
An optimal operation of the intake valves and the exhaust valves depends on rotation speed of the engine. That is, an optimal lift or optimal opening/closing timing of the valves depends on rotation speed of the engine. In order to achieve such an optimal valve operation which depends on the rotation speed of the engine, various research, such as designing a plurality of cams and a variable valve lift (VVL) to change valve lift according to engine speed, has been undertaken.
The existing continuous variable valve lifter (CVVL) does not directly adjust air volume difference between cylinders, but instead adjusts valve lift difference.
That is, air volume differences are preferably adjusted by adjusting the valve lift differences. However, air volume differences still exist even with the same lifter due to manufacturing deviations in peripheral parts of intake valves, and there are limits on how precise the adjustment can be.
A conventional method for valve lift difference adjusts thickness of a shim/spacer inserted in a shaft. However, adjusting lift difference is difficult since the shim/spacer cannot be replaced while the CVVL is in operation.
Moreover, to check if lift difference adjustment has been done to a desired level, it is necessary to stop the CVVL, replace the shim/spacer with a part having a desired thickness, and operate the CVVL, which is cumbersome.
In addition, air volume differences still exist due to manufacturing deviations in peripheral parts of intake valves even after adjusting the lift difference to some extent. Therefore, precisely adjusting an air volume difference with the conventional lift difference adjustment method has limitations.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the present disclosure, and therefore it may contain information that does not form the prior art already known in this country to a person of ordinary skill in the art.